Hidden micromirror support structure

ABSTRACT

Methods and apparatus for use with a micromirror element includes a micromirror a micromirror having a substantially flat outer surface disposed outwardly from a support structure that is operable to at least partially support the micromirror. The support structure includes at least one layer overlying at least two discrete planes that are both substantially parallel to the outer surface of the micromirror. In one particular embodiment, the support structure includes annular-shaped sidewalls that encapsulate a photoresist plug.

TECHNICAL FIELD

This invention relates in general to spatial light modulators and, inparticular, to a digital micromirror device having an improvedmicromirror support structure and a method of manufacturing the same.

BACKGROUND

A vast array of semiconductor devices utilize physical vapor deposition(PVD) techniques in conjunction with deep ultraviolet (DUV)photolithography. PVD is a group of vacuum coating techniques used todeposit thin films of various materials onto various surfaces (e.g., ofsemiconductor wafers) by physical means, as compared to chemical vapordeposition. DUV is used for very fine resolution photolithography, aprocedure where a chemical known as a photoresist is exposed to UVradiation which has passed through a mask. The light allows chemicalreactions to take place in the photoresist, and after development (astep that either removes the exposed or unexposed photoresist), ageometric pattern which is determined by the mask remains on the sample.Further steps may then be taken to “etch” away parts of the sample withno photoresist remaining.

The processing of microelectromechanical systems (MEMS) oftenincorporates PVD techniques in conjunction with photolithography. Inaddition, MEMS processing frequently includes structures that are spacedapart by rigid supports.

SUMMARY OF THE EXAMPLE EMBODIMENTS

In one embodiment, a micromirror element comprises a micromirror havinga substantially flat outer surface disposed outwardly from at least onesupport structure. The at least one support structure is operable to atleast partially support the micromirror. In addition, the at least onesupport structure comprises at least one layer overlying at least twodiscrete planes that are both parallel to the outer surface of themicromirror.

In a method embodiment, a method of forming a micromirror elementcomprises forming a sacrificial layer and selectively removing a portionof the sacrificial layer to form at least one micromirror support via.The method further comprises forming a first portion of a micromirrorsupport structure within the at least one micromirror support via and asecond portion of the micromirror support structure outwardly from thesacrificial layer. In addition, the method comprises forming asubstantially flat micromirror surface outwardly from the first andsecond portions of the micromirror support structure.

Technical advantages of some embodiments of the invention may includeincreasing the contrast ratio of the DMD by increasing the fill-factorratio of total reflective surfaces while minimizing stray reflections.In some embodiments, a substantially sold micromirror support structuremay enhance structural rigidity. Additionally, some embodiments maycomprise micromirror support structure having increased conductivesidewall thickness, thereby potentially enhancing conductivity betweenconductive layers. Some particular embodiments may include the samenumber of process steps as conventional DMD processing.

It will be understood that the various embodiments of the presentinvention may include some, all, or none of the enumerated technicaladvantages. In addition other technical advantages of the presentinvention may be readily apparent to one skilled in the art from thefigures, description, and claims included herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and featuresand advantages thereof, reference is now made to the followingdescription, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a block diagram of one embodiment of a portion of a displaysystem;

FIGS. 2A and 2C through 2D are cross-sectional views illustrating oneexample of a method of forming a portion of a digital micromirrordevice; and

FIG. 2B is a perspective view illustrating one example of a method offorming a portion of a digital micromirror device.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Particular examples and dimensions specified throughout this documentare intended for example purposes only, and are not intended to limitthe scope of the present disclosure. In particular, this document is notintended to be limited to a particular spatial light modulator device,such as, a digital micromirror device. Moreover, the illustrations inFIGS. 1 through 2D are not necessarily drawn to scale.

FIG. 1 is a cross-sectional block diagram of one embodiment of a portionof a light processing system 10 that may be used with other embodimentsof the invention. The display system 10 of FIG. 1 includes a lightsource module 12 capable of generating illumination light beams 14.Light beams 14 are directed from light source module 12 to a modulator16. Modulator 16 may comprise any device capable of selectivelycommunicating at least some of the received light beams along aprojection light path 18. In various embodiments, modulator 16 maycomprise a spatial light modulator, such as, for example, a liquidcrystal display, a light emitting diode modulator, or a liquid crystalon silicon display. In the illustrated embodiment, however, modulator 16comprises a digital micromirror device (DMD).

A DMD is a microelectromechanical device comprising an array of hundredsof thousands of tilting digital micromirrors. In a flat or neutralstate, each micromirror may be substantially parallel to projection lens24. Each micromirrors may be tilted, for example, to a positive ornegative angle corresponding to an “on” state and an “off” state. Inparticular embodiments, the micromirrors may tilt, for example, from +12degrees to a −12 degrees. Although particular embodiments, may havemicromirrors that tilt from +12 degrees to a −12 degrees, any otherappropriate tilt angle may be used without departing from the scope ofthe present disclosure. To permit the micromirrors to tilt, one or moresupport structure attaches each micromirror to one or more hinges. Eachhinge is mounted on support structure and spaced by means of an air gapover underlying control circuitry. The control circuitry provides thedesired voltages to the respective layers, based at least in part onimage data 20 received from a control module 22. In various embodiments,modulator 16 is capable of generating various levels or shades for eachcolor received.

Electrostatic forces cause each micromirror to selectively tilt.Incident illumination light on the micromirror array is reflected by the“on” micromirrors along projection path 18 for receipt by projectionlens 24. Additionally, illumination light beams 14 are reflected by the“off” micromirrors and directed on off-state light path 26 toward lightabsorber 28. The pattern of “on” versus “off” mirrors (e.g., light anddark mirrors) forms an image that is projected by projection lens 24.

Light source module 12 includes one or more lamps or other light sourcescapable of generating and focusing an illumination light beam. Althoughdisplay system 10 is described and illustrated as including a singlelight source module 12, it is generally recognized that display system10 may include any suitable number of light sources modules appropriatefor generating light beams for transmission to modulator 16.

As discussed above, display system 10 includes a control module 22 thatreceives and relays image data 20 to modulator 16 to effect the tiltingof micromirrors in modulator 16. Specifically, control module 22 mayrelay image data 20 that identifies the appropriate tilt of themicromirrors of modulator 16. For example, control module 22 may sendimage data 20 to modulator 16 that indicates that specific micromirrorsof modulator 16 should be positioned in the “on” state. Accordingly, themicromirrors may be positioned at a tilt angle on the order ofapproximately +12 degrees, as measured from projection path 18.Alternatively, control module 22 may send image data 20 to modulator 16that indicates specific micromirrors should be positioned in the “off”state. As such, the micromirrors may be positioned at a tilt angle onthe order of approximately −12 degrees, as measured from projection path18.

For conventional DMDs, the formation of micromirror support postscreates a hollow opening in the center of the micromirror that inhibitsoptical performance and reliability for a variety of reasons. In manyinstances, prior attempts to support a micromirror without this hollowopening complicated DMD processing and increased production costs.Accordingly, teachings of some embodiments of the invention recognizeddesign and processing techniques that provide a homogeneously flatmicromirror surface without significantly increasing production costs orprocess steps. In such embodiments, the homogeneous outer surface ofeach micromirror may increase the contrast ratio of the DMD byincreasing the fill-factor ratio of total reflective surfaces whileminimizing stray reflections. In some embodiments, a substantially solidmicromirror support structure (e.g., support structure 275 of FIG. 2D)may enhance structural rigidity. Some embodiments may include amicromirror support structure having increased micromirror postthicknesses (e.g., micromirror posts 270 in FIG. 2D), therebypotentially enhancing conductivity between conductive layers (e.g.,between hinge layer 210 and micromirror layer 260 in FIG. 2D). As willbe shown in FIGS. 2A through 2C, some embodiments may not even requireincreasing the total number of process steps associated withconventional DMD processing.

FIG. 2A shows a cross-sectional view of a portion of DMD 200 after theformation of a sacrificial layer 220 disposed outwardly from hinge layer210, and after formation of a micromirror support vias 230 withinsacrificial layer 220. Although sacrificial layer 220 and hinge layer210 are shown as being formed without interstitial layers between them,such interstitial layers could alternatively be formed without departingfrom the scope of the present disclosure. Sacrificial layer 220 maycomprise, for example, oxide, hardened photoresist, or other materialthat may be selectively removed. That is, sacrificial layer 220 can beselectively removed using any number of processes, such as, for example,by performing a plasma-ash that does not significantly affect hingelayer 210.

Forming sacrificial layer 220 may be effected through any of a varietyof processes. In one non-limiting example, sacrificial layer 220 can beformed by depositing an oxide or photoresist material. In some cases,sacrificial layer 220 can be etched or polished back to a desiredthickness, such as, for example, by using a chemical mechanical polish(CMP) technique. In particular embodiments, sacrificial layer 220 maycomprise a final thickness of approximately 1 μm. In other embodiments,sacrificial layer 220 may comprise a final thickness greater than 1 μmor less than 1 μm.

Forming micromirror support vias 230 associated with a particularmicromirror may be effected through any of a variety of processes. Forexample, micromirror support vias 230 may be formed by removingsubstantially all of a portion of sacrificial layer 220. In thisparticular embodiment, micromirror support vias 230 are formed bypatterning and etching sacrificial layer 220 using deep ultravioletlight (DUV) photolithography. In this particular embodiment, micromirrorsupport vias 230 comprise widths (x and y) of approximately 0.35 μmeach. Although micromirror support vias 230 are both approximately 0.35μm wide in this example, any appropriate widths or combination of widthsmay be used without departing from the scope of the present disclosure.

FIG. 2B is a perspective view illustrating a particular exampleembodiment of forming a portion of a digital micromirror (DMD) device200 after selectively removing an annular-shaped micromirror support via230 from a sacrificial layer 220 disposed outwardly from a hinge layer(e.g., hinge layer 210 in FIG. 2A). Sacrificial layer 220 may comprise,for example, materials substantially similar in composition as thesacrificial layer 220 of FIG. 2A. Likewise, the partial removal ofsacrificial layer 220 may be effected by any of a variety of processessimilar to those disclosed in FIG. 2A. In this particular embodiment,the partial removal of sacrificial layer 220 forms a sacrificial layerplug 225 that is separated from sacrificial layer 220 by a width ofapproximately 0.35 μm (e.g., widths x and y). As will be shown,subsequent layers disposed outwardly from sacrificial layer 220 mayencapsulate sacrificial layer plug 225 thereby forming a “filled via” ora substantially solid support structure. Although this particularembodiment uses an annular-shaped micromirror support via 230, othershapes or combinations of discrete support vias may be used withoutdeparting from the scope of the present disclosure. For example,micromirror support via 230 may alternatively be C-shaped or include aplurality of support posts or pillars.

FIG. 2C shows a cross sectional view of DMD 200 after formation of amicromirror support layer 240 outwardly from sacrificial layer 220 andafter formation of the support sidewalls 250,255 within support vias230. Although micromirror support layer 240 and sacrificial layer 220are shown as being formed without interstitial layers between them, suchinterstitial layers could alternatively be formed without departing fromthe scope of the present disclosure. Support sidewalls 250,255supporting a particular micromirror comprise outer sidewalls 250 andinner sidewalls 255. In this particular embodiment, the support bases270 connect support sidewalls 250,255 and electrically interconnectmicromirror support layer 240 to hinge layer 210. The term “micromirrorsupport structure” 275 should be interpreted as generally defining thevolume circumscribed by outer sidewalls 250. In this particular example,micromirror support structure 275 overlies two parallel planes asindicated by reference numbers 235,270. In particular embodiments, themicromirror support structure 275 may have voids disposed inwardly froma flat surface. In other embodiments, micromirror support structure maybe substantially solid.

Micromirror support layer 240 may comprise, for example, aluminum,silicon, polysilicon, tungsten, nitride, and/or combinations of thepreceding. In this example, micromirror support layer 240 comprises areflective material, such as, for example, aluminum, an aluminum alloy,or any other appropriate reflective material. Although micromirrorsupport layer 240 comprises a reflective material in this example, anyother desired conductive material can be used without departing from thescope of the present disclosure. Forming micromirror support layer 240may be effected through any of a variety of processes. For example,micromirror support layer 240 can be formed by depositing an anisotropicphysical vapor deposition (PVD) layer of an aluminum alloy. In onenon-limiting example, micromirror support layer 240 can be formed bydepositing metal to a thickness of approximately 820 angstroms. Althoughthis example uses a thickness of approximately 820 angstroms, otherappropriate thicknesses may be used without departing from the scope ofthe present disclosure. For example, in alternative embodiments,micromirror support layer 240 may be sufficiently thick to completelyfill micromirror support vias 230 and form an outermost surface that issubstantially flat. In addition, in such alternative embodiments,sidewalls 250 and 255 may join to form one common sidewall.Significantly, such alternative embodiments may not include anadditional metal deposition step as illustrated in FIG. 2D.

FIG. 2D shows a cross sectional view of DMD 200 after formation of amicromirror layer 260 outwardly from micromirror support layer 240.Although micromirror layer 260 and micromirror support layer 240 areshown as being formed without interstitial layers between them, suchinterstitial layers could alternatively be formed without departing fromthe scope of the present disclosure.

Micromirror layer 260 may comprise, for example, materials substantiallysimilar in composition as micromirror support layer 240 of FIG. 2C.Forming micromirror layer 260 may be effected through any of a varietyof processes. For example, micromirror layer 260 may be formed bydepositing an isotropic physical vapor deposition (PVD) layer of analuminum alloy. In this particular non-limiting example, micromirrorsupport layer 260 can be formed by depositing aluminum to a thickness ofapproximately 2480 angstroms. Although this example uses a micromirrorlayer 260 thickness of approximately 2480 angstroms, other appropriatethicknesses may be used without departing from the scope of the presentdisclosure. An appropriate micromirror layer 260 thickness at leastincludes thicknesses sufficient to form a substantially flat outermostsurface 280 disposed outwardly from micromirror support structure 275.In this embodiment, surface 280 is substantially coplanar to theremainder of the outer micromirror surface.

As discussed above with regard to modulator 16 of FIG. 1, DMD 200 mayinclude an array of hundreds of thousands of tilting micromirrors. Inthis particular example, at some point one or more micromirrors areformed within micromirror layer 260. Forming the micromirrors may beeffected through any of a variety of processes. For example, themicromirrors may be formed by removing portions of layers 240,260. Inthis particular non-limiting embodiment, the micromirrors are formed bypatterning and etching micromirror layer 260 and micromirror supportlayer 240 simultaneously.

Although the present invention has been described in severalembodiments, a myriad of changes, variations, alterations,transformations, and modifications may be suggested to one skilled inthe art, and it is intended that the present invention encompass suchchanges, variations, alterations, transformations, and modifications asfalling within the spirit and scope of the appended claims.

1. A light processing system comprising: a light source operable togenerate light; a digital micromirror device comprising a plurality ofpixel elements each comprising a micromirror operable to selectivelyreflect light from the light source in response to receiving a signal;for each micromirror, at least one micromirror support structure and asubstantially flat outer surface disposed outwardly from the at leastone support structure, the at least one support structure operable to atleast partially support the micromirror and comprising at least onelayer overlying at least two discrete planes that are both substantiallyparallel to the outer surface of the micromirror; a plurality of opticalelements operable to direct the selectively reflected light from thedigital micromirror device along an optical path; and a signal processorcapable of providing the signal to the digital micromirror device. 2.The light processing system of claim 1, wherein the at least onemicromirror support structure comprises annular-shaped sidewalls.
 3. Thelight processing system of claim 2, wherein at least a portion of theannular-shaped sidewalls comprise nonconductive material.
 4. The lightprocessing system of claim 1, wherein the at least one support structurecomprises a plurality of layers.
 5. The light processing system of claim1, wherein the at least one support structure is formed with voidstherein.
 6. A micromirror element comprising: at least one supportstructure; a micromirror having a substantially flat outer surfacedisposed outwardly from the at least one support structure, the at leastone support structure operable to at least partially support themicromirror; and wherein the at least one support structure comprises atleast one layer overlying at least two discrete planes that are bothsubstantially parallel to the outer surface of the micromirror.
 7. Themicromirror element of claim 6, wherein the at least one layer comprisesannular-shaped sidewalls.
 8. The micromirror element of claim 7, whereinat least a portion of the annular-shaped sidewalls comprisenonconductive material.
 9. The micromirror element of claim 6, whereinthe at least one support structure comprises voids.
 10. The micromirrorelement of claim 6, wherein the at least one support structure comprisesa plurality of layers.
 11. The micromirror element of claim 10, whereinthe at least one layer comprises an anisotropic physical vapordeposition layer.
 12. The micromirror element claim 10, comprising: atleast one isotropic physical vapor deposition layer disposed outwardlyfrom the anisotropic physical vapor deposition layer.
 13. A method offorming a micromirror element comprising: forming a sacrificial layer;forming at least one micromirror support via by selectively removing aportion of the sacrificial layer; forming a first portion of amicromirror support structure within the at least one micromirrorsupport via and a second portion of the micromirror support structureoutwardly from the sacrificial layer; and forming a substantially flatmicromirror surface outwardly from the first and second portions of themicromirror support structure.
 14. The method of claim 13, whereinselectively removing at least a portion of the sacrificial layercomprises selectively removing an annular-shaped portion.
 15. The methodof claim 14, wherein forming a second portion of the micromirror supportstructure outwardly from the sacrificial layer comprises encapsulating aportion of the sacrificial layer within annular-shaped sidewalls of thesupport structure.
 16. The method of claim 13, wherein forming the firstportion of the micromirror support structure within the at least onemicromirror support via comprises filling the micromirror support viawith the first portion of a micromirror support structure.
 17. Themethod of claim 16, further comprising: filling the micromirror supportvia with a single layer having sufficient thickness to form asubstantially flat outer surface disposed outwardly from the micromirrorsupport via.
 18. The method of claim 16, further comprising: filling themicromirror support via with a plurality of layers.
 19. The method ofclaim 18, wherein filling the micromirror support via with a pluralityof layers comprises forming an anisotropic physical vapor depositionlayer.
 20. The method of claim 19, further comprising: forming anisotropic physical vapor deposition layer outwardly from the anisotropicphysical vapor deposition layer.